Rapper



pr 1962 J. w. PENNINGTON RAPPER Filed April 10, 1958 United StatesPatent f 3,030,753 RAPPER John W. Pennington, West Friendship, MtL,assiguor to Koppers Company, Inc, a corporation of Delaware Filed Apr.10, 1958, Ser. No. 727,616 2 Claims. (Cl. 55-112) This invention relatesto an electrostatic precipitator and particularly to a pneumatic rapperfor electrode structures of electrostatic precipitators.

Conventionally, impulse rappers of the mechanical, pneumatic orelectromagnetic types have been used to effect transient vibrations ofhigh intensity in electrodes suspended in the prevailing particle-ladengas flow in electrostatic precipitators. These vibrations cause thematemial deposited on the electrodes to fall into a hopper at the bottomof the precipitator. The rappers as known heretofore, however, oftensupplied the electrode with vibrations that were too intense, thuscausing the material deposited on the electrodes to break up into veryfine particles. Accordingly, much of the material which vibrated loosefrom the electrodes was re-entrained in the prevailing gas stream in theprecipitator and carried out of the precipitator.

It has been discovered, according to this invention, that rappers whichcause vibrations of more continuous duration and lower intensity areadvantageous for vibrating the electrodes because such rapperseffectively remove deposited material from the electrodes and greatlyreduce re-entrainment of the loosened material in the gas.

An object of the invention, therefore, is to provide the electrodes ofan electrostatic precipitator with a rapper having a novel rappingmotion and provision for keeping dislodged material from re-entering thegas stream.

Another object is to provide such a rapper which requires nolubrication.

This invention contemplates a novel rapper that is pneumaticallyactuated for rapidly reciprocating a hammer in a rapper housing toeffect vibrations of low intensity and high frequency to the suspendedelectrodes of an electrostatic precipitator and has a provision forlowering the friction between the hammer and the housing so thatlubrication is not required. In another aspect, this inventioncontemplates applying, with the aid of an epoxy resin, a low frictionmaterial to the hammer of the rapper so as to form a firmly bondedveneer which requires no lubrication.

The above and further objects and novel features of the invention willappear more fully from the following detailed description when the sameis read in connection with the accompanying drawings. It is to beexpressly understood, however, that the drawings are not intended as adefinition of the invention but are for the purpose of illustrationonly.

FIG. 1 shows a partial cross-section of an embodiment of the novelrapper of this invention connected to a resiliently mounted electrode ofan electrostatic precipitator.

FIG. 2 is a partial cross-section showing details of the novel rapper ofFIG. 1.

FIG. 3 shows a partial cross-section of the hammer of FIG. 2.

Referring to FIG. 1, the novel rapper 11 or vibrator, as it is sometimescalled, is connected to an electrode 13. conventionally, electrode 13has wires or plates (not shown) suspended therefrom in the path of aprevailing particle-laden gas stream passing through a precipitatorshell 15 under pressure. Electrode 13 is supported by a nut 17 that islocked to electrode 13, as by a nut 19, and rests on a resilient spring21 interposed between a plate 23 and the nut 17. Plate 23 is attached tothe top of an insulator 25 which, by suitable means well known in theart, is mounted on the outside of the shell 15.

Rapper 11 is rigidly connected to the collecting electrode 13 by meansof a suitable nut 27 threaded on the top of the electrode 13. Theelectrode 13 extends into the precipitator shell 15 through a suitablehole 29 in plate 23 and a hole 31 in the precipitator shell 15. Thediameter of hole 31 substantially corresponds to the inside diameter ofthe insulator 25. A conventional tubular sparking shield 33 is suspendedfrom the inside of shell 15 around electrode 13. The electrode 13 andthe rapper 11 are thus electrically insulated from the shell 15 as wellas being resiliently supported so that vibrations are transmitted fromthe rapper 11 to the electrode 13 without undue damping effects in theelectrode supporting structure as would be present with conventionalrigid supports for the electrode.

Housing 35 surrounds the rapper 11 and insulator 25 with a chamber '37and prevents the leakage of gas from the inside of the precipitatorshell 15 to the atmosphere. The housing 35 may also have a conventionalinsulator (not shown) attached through the side thereof in a fluidtightmanner and a conventional electrical connection may be held in thisinsulator in a conventional fluid-tight manner so that this electricalconnection may be attached from the electrode 13 to a suitableelectrical source (not shown) to give the electrode 13 an electricalpotential as required.

Air is supplied to the rapper 11 through a hole 39 in the side of therapper 11 from a suitable source (not shown) through pipe 41, regulatorvalve 43, pipe 45, filter 47, pipe 49, hand valve 51, pipe 53, trap 55,pipe 57, solenoid operated valve 59, pipe 61, union 63, pipe 65,connection 67, tube 69 and hose 71 which has conventional fittings whichare threaded into hole 39 and the end of tube 69. Suitable pressuregauges (not shown) and drain lines for excess moisture may be suppliedin a conventional manner. With the valves mentioned and conventionalactuating means therefor air pressure to the rapper 11 may be regulatedto obtain desired vibration frequencies and intensities from the rapper.Suitable control means such as a conventional timer may also be providedtogether with solenoid valve 59 to start and stop the rapping of rapper11. This may be done so that the rapper is on and off at suitableintervals.

Advantageously air supply tube 69 is suspended from connection 67 to apoint in a plane near the bottom of the rapper 11 and the connection 67is attached to the top of the housing 35 in a fluid-tight manner. Thehose 71 is advantageously arranged away from air exhaust ports 73 and 75(FIG. 2) of the rapper 11. A rubber hose may extend from connection 67to hole 39 in the rapper 11, but in this event, any bend in the hosemust not be less than eight inches in diameter to prevent unduerestriction in the hose and wear at the fittings for the hose such aswouldbe caused by sharper bends.

Referring now to FIG. 2, rapper 11 comprises a rapper housing 77hereinafter called a cylinder 77 with external ports 73 and 75 andinternal communicating vents 79 and 81. Cylinder 77 at one end is closedby a plate 83 and the other end is closed by a plate 85 that is infrictional contact with a base 87. Cylinder 77 is advantageously heldwithin end plates 83 and 85 and base 87 by four rods 89 disposed in fourstraight-through holes 91, four top nuts 93, four bottom nuts and foursprings 97 interposed between the nuts 93 and plate 83. Springs 97surround rods 89 and abut washers 99 at one end and indentations 101 inplate 83 at the other end. A suitable pin 103 is inserted in bothcylinder 77 and plate 85 to prevent their relative movement. One end ofthe electrode 13 is partially conical in cross-section and this end ofelectrode 13 extends through a conical opening in base 87 and is securedthereto by nut 27 in a hollow 105 in plate 85.

3 A hammer 107 reciproeates within the cylinder 77. This hammer 107(FIG. 3) has raised end portions 109 and 111, bearing lands 113 and 115and a groove 117 between the lands. Hammer 107 is advantageously made ofSA 1030 steel which has been carburized for eight to ten hours at 1700F., oil quenched at 1600 F., and then stress relieved at 350 F. forthree hours. This gives the hammer the required toughness and a Rockwellscale C hardness of between 52-58. Other materials, however, may also beused provided they have the necessary toughness and hardness.

A conventional steel coil spring 119 having one end of smaller diameterthan the other end contacts the hammer 107 and the plate 85. The springend of smaller diameter fits over the bottom raised portion 111 ofhammer 107 and the end of larger diameter contacts the inside of plate85 so that raised portion 111 may strike plate 85. Thus, spring 119 canexert an upward force on the hammer 107.

In accordance with this invention, to reduce the friction between thehammer 107 and the inside bearing surface 120 of cylinder 77, it hasbeen found advantageous to bond glass-filled polytetrafiuoroethylene tothe lands 113 and 115 and it has been found advantageous to usepolytetrafluoroethylene in the form. of a suitably treated tape, such asthe glass-filled polytetrafluoroethylene tape purchased from theEthylene Chemical Corp. of Summit, New Jersey. Polytetrafluoroethylenehas the chemical structure as follows:

In its polymerized form, polytetrafiuoroethylene has the advantageousproperties of low coefiicient of friction, toughness and flexibilityover a wide range of temperatures. The granular polymer is supplied in apowdered form which can be extruded or molded easily in a conventionalmanner. To give added strength to the polytetrafluoroethylene choppedglass fibers, free of sizing in the amount of about 23% to 25% byweight, are advantageously mixed with powdered polytetrafluoroethyleneand this mixture of chopped glass and powdered polytetrafluoroethyleneis extruded into a suitable solid shape. This extrusion is skived into acoiled tape whose inside coil is not less than twelve inches indiameter. This coiled tape is then stress relieved by heating to 425 F.for three hours in a conventional oven and thereafter cooled to roomtemperature in the oven. This glass-filled polytetrafiuoroethylene tapeis advantageously approximately 4 to & of an inch thick as commerciallyavailable. If this tape is thinner than & of an inch it may not wearsatisfactorily and if it be thicker than A of an inch the leading edgemay flow or stretch in operation. This tape is then formed by cuttinginto substantially circular rings 121 of /2 to 1 inch widths and ofinside diameters corresponding to the outside diameter of the bearinglands 113 and 115.

To provide optimum results in bonding these glassfilledpolytetrafluoroethylene rings 121 to the hammer 107, the surface of thebearing lands 113 and 115 are threaded with threads 123. The hammer 107is then cleaned of any 'rust, grease, organic coatings or dirt byblasting, as with liquid and fine sand, and dipping the hammer in avolatile solvent such as carbon tetrachloride.

The rings 121 are bonded to the threaded bearing lands 113 and 115 andthe ends of the rings 121 are joined with an epoxy resin. For thispurpose it is advantageous to use Palmer Products epoxy resin No. 6035which is thinned with Palmer Products thinner No. BS-1022, both beingsupplied by Palmer Products of Worchester, Pa. The thinned resin isapplied to the surface of the bearing lands 113 and 115, and the rings121 are held firmly to the bearing lands 113 and 115, having the epoxyresin thereon, by a conventional sheet metal sleeve and two hose clamps(not shown). The assembly is placed in a conventional oven for curing atroom temperature and brought to 175 F. and maintained at thistemperature for five hours. Thereafter, the temperature is raised to 250F. and maintained at 250 F. for one additional hour. The assembly isthen cooled to room temperature, for example, either in the oven or instill air. The cured resin is extremely hard, and advantageously theexcessive cured resin, if present, is removed and the glass-filledpolytetrafluoroethylene tape, now in the form of a veneer, is finishedto size by machining. It has been found that, in bonding theglass-filled polytetrafiuoroethylene rings 121 to the hammer 107 in themanner described, no growth in the dimensions of the tape occurs tocause seizing of hammer 107 in cylinder 77. Rates of wear of theglassfilied polyetetrailuoroethylene rings 121 tend to be constant,uniform and slow so that substantially constant rapper vibrationintensities are maintained over long periods of time.

In operation, rings 121 around bearing lands 113 and are in frictionalsealing contact with the inside bearing surface of cylinder 77. Whenthere is no air under pressure being supplied to the rapper 11 throughhole 39 the hammer portion 109 is held in contact with the inside ofplate 83 by spring 119. When the hammer 107 is in contact with the plate83 ring 121 around bearing land 1.13 covers ports 73 so as to close theupper inside half of cylinder 77 from the atmosphere and air may flowfrom hole 39 through groove 117 and vent 79 to the upper inside half ofcylinder 77. Also, when hammer portion 109 is in contact with plate 83,ring 121 around bearing land 115 closes vent 81, so that air cannotcommunicate to the lower inside half of cylinder 77 from hole 39 throughgroove 117 and vent 81, and ring 121 around bearing land 115 does notcover ports 75 so that the lower inside half of cylinder 77 is vented tothe atmosphere through ports 75. Thus, when the hammer 107 is in contactwith plate 83 and air under pressure is supplied through hole 39, air issupplied through vent 79 to the upper inside half of cylinder 77, airpressure on the top of hammer 107 increases and air pressure on thelower half of the hammer is vented to the atmosphere. This pressuredifferential on the hammer overcomes the resistance of spring 119 andthe hammer is impelled downwardly so that portion 111 strikes the insideof plate 85. As the hammer 107 moves downwardly the ring 121 aroundbearing land 113 uncovers ports 73 so as to communicate the upper insidehalf of cylinder 77 with the atmosphere and this ring 121 around bearingland 113 also closes the vent 79 so that no air can communicate fromhole 39 through groove 117 and vent 79 to the upper inside half ofcylinder 77. Also, as the hammer 107 moves downwardly, the ring 121around bearing land 115 covers the ports 75 so as to close the lowerinside half of cylinder 77 from the atmosphere and opens vent 81 so thatair can communicate from hole 39 to the lower inside half of cylinder 77through groove 117 and vent 81. Thus when the hammer 107 is in contactwith plate 85 and air under pressure is supplied through hole 39 air issupplied through vent 81 to the lower inside half of cylinder 77,pressure on the bottom of hammer 107 increases and pressure on the upperhalf of the hammmer is vented to the atmosphere. This pressuredifierential on the hammer 107 together with the force of spring 119impels the hammer upwardly so that portion 109 strikes the inside ofplate 83. As long as air under pressure is supplied through hole 39 thehammer will reciprocate rapidly and continuously in the manner describedabove. Advantageously this reciprocation is repeated at approximatelysixty cycles per second. This rate of reciprocation, however, can bevaried by increasing or decreasing the air pressure and flow throughhole 39 by means of regulator valve 43 and hand valve 51. This rapidreciprocation of hammer 107' transmits vibrations from the rapper 11 tothe electrode 13. For example, every time the hammer 107 strikes one ofthe end plates 83 or 85 the terminal energy of the hammer, which isdetermined by the mass and final velocity of the hammer is imparted tothe electrode 13 via the base 8 7 so that vibrations are imparted to theelectrode 13. Advantageously the intensity of the vibrations thusimparted to the electrode 13 is great enough to remove the depositedmaterial from the electrode 13 but not great enough to cause the removedmaterial to be broken up into fine particles so as to causerte-entrainment. These vibrations can be increased or decreased to thedesired intensity by increasing or decreasing the air pressure and flowrate through the hole 39 by means of regulator valve 43 and the handvalve 51.

Tests on hammers having glass-filled polytetrafluoroethylene veneerapplied in the above described manner to a hammer which reciprocates, asdescribed, indicate that such a veneer can be used over greatly extendedperiods of time under normal operating conditions without detrimentaleffects on the bonded veneer or the cylinder bearing surface. Thesetests indicate that such pistons give vibrations of substantiallyuniform intensities at elevated temperatures for long periods of timewithout any lubrication whatsoever.

What is claimed is:

1. In an electrostatic precipitator for removing particles from a gasstream having elevated ambient temperatures, a casing and a plurality ofelectrodes suspended within said casing; the improvement comprisingmeans for vibrating said electrodes, said means being aresiliently-mounted vibrator including a cylinder having end-plateclosures, a hammer mounted for reciprocation within said cylinderbetween said end-plate closures and having two spaced raised bearinglands formed thereon, said lands having threadlike grooves formed in theouter surface thereof, each of said bearing lands having a single layerof fiber-filled polytetrafluoroethylene tape bonded to said threadedouter surface for forming a lubricantfree bearing surface, said layerhaving a thickness between about and about of an inch and means forcausing said hammer to reciprocate, said hammer striking said end-plateclosures with substantially equal impact.

2. In an electrostatic precipitator for removing particles from a gasstream having elevated ambient temperatures, a casing and a plurality ofelectrodes suspended within said casing; the improvement comprisingmeans for vibrating said electrodes, said means being aresiliently-mounted vibrator including a cylinder having end-plateclosures, a hammer mounted for reciprocation within said cylinderstriking said end-plate closures and having two spaced bearing landsformed thereon, said lands having threadlike grooves formed in the outersurface thereof, each of said bearing lands having a single layer offiberfilled polytetrafluoroethylene tape of approximately to eg of aninch thickness bonded to said threaded outer surface for forming alubricant-free bearing surface, means for causing said hammer toreciprocate, said hammer striking said end-plate closures withsubstantially equal impact and means for controlling the intensity ofvibration of said hammer.

References Cited in the file of this patent UNITED STATES PATENTS2,030,936 Pickop Feb. 18, 1936 2,702,090 Brown Feb. 15, 1955 2,777,535Hull Jan. 15, 1957 2,809,130 Rappaport Oct. 8, 1957 2,817,562 FlemingDec. 24, 1957 2,828,236 West Mar. 25, 1958 2,847,391 Wheeler Aug. 12,'1958

1. IN AN ELECTROSTATIC PRECIPITATOR FOR REMOVING PARTICLES FROM A GASSTREAM HAVING ELEVATED AMBIENT TEMPERATURES, A CASING AND A PLURALITY OFELECTRODES SUSPENDED WITHIN SAID CASING; THE IMPROVEMENT COMPRISINGMEANS FOR VIBRATING SAID ELECTRODES, SAID MEANS BEING ARESILIENTLY-MOUNTED VIBRATOR INCLUDING A CYLINDER HAVING END-PLATECLOSURES, A HAMMER MOUNTED FOR RECIPROCATION WITHIN SAID CYLINDERBETWEEN SAID END-PLATE CLOSURES AND HAVING TWO SPACED RAISED BEARINGLANDS FORMED THEREON, SAID LANDS HAVING THREADLIKE GROOVES FORMED IN THEOUTER SURFACE THEREOF, EACH OF SAID BEARING LANDS HAVING A SINGLE LAYEROF FIBER-FILLED POLYTETRAFLUOROETHYLENE TAPE BONDED TO SAID THREADEDOUTER SURFACE FOR FORMING A LUBRICANTFREE BEARING SURFACE, SAID LAYERHAVING A THICKNESS BETWEEN ABOUT 3/32 AND ABOUT 1/4 OF AN INCH AND MEANSFOR CAUSING SAID HAMMER TO RECIPROCATE, SAID HAMMER STRIKING SAIDEND-PLATE CLOSURES WITH SUBSTANTIALLY EQUAL IMPACT.